This project deals with studies in chemical carcinogenesis. ESR- spin-labelling techniques are being applied to study the mechanism of binding of chemical carcinogens to cellular components. The technique has allowed direct verification of intercalative mechanisms of a series of aromatic amine carcinogens in DNA. The method has been used to monitor competitive binding of carcinogens and sex specific steroid hormones to endoplasmic reticulum membranes. Studies are also underway on the relationship between a non heme iron Fe 2 ion - NO complex induced in liver of rats fed nitrite ion and carcinogenesis. Studies on the formation of nitrosamines from NO-heme complexes are also underway.